Various embodiments of a method for manufacturing reinforced beams are described herein. In particular, the embodiments described herein relate to an improved method for manufacturing pre-stressed reinforced beams having bonded tendons.
Conventional glued-laminated (glulam) beams often fail in bending-induced tension. To strengthen glulam beams and delay or prevent such bending-induced tension failure, attempts have been made to reinforce glulam beams with different types of tensile reinforcement, such as fiber reinforced polymer (FRP) or glass fiber reinforced polymer (GFRP) on the tension face of the beam. Such FRP reinforcement offers good corrosion resistance and has a high strength-to-weight ratio. Increases in bending capacity of 50 percent or more when compared to unreinforced glulam have been achieved with FRP tensile reinforcement. The use of FRP reinforcement permits the use of glulam beams made with low-grade laminations and/or a reduction in wood volume.
It is further known that the strength of a glulam beam may be further increased if the tensile reinforcement is pre-tensioned prior to being bonded to the glulam. The bonding of the tensile reinforcement to the glulam beam pre-stresses the reinforced beam. This pre-stressing results in significant initial compressive stresses in the bottom of the reinforced beam that counteract the tensile bending stresses caused by external loads. It has been observed that longitudinal cracks may form at the longitudinal ends of the reinforced beam. The cracks are the result of high stresses in the vertical direction. Horizontal stresses, or shear stresses, and the vertical stresses, are known to be higher at the longitudinal ends than at the center of the reinforced beam. The above notwithstanding, it would be advantageous to provide an improved method for manufacturing a reinforced beam.